The present invention relates to the field of steering wheel devices used, purely by way of example, for steering motor vehicles, handling plant, or civil engineering works vehicles or any other type of vehicle requiring a control handwheel.
Conventionally, a steering wheel is connected to a shaft, for example a steering column, which, depending on the type of steering used, directly turns the steering mechanism in the case of mechanical steering, distributors in the case of hydraulic steering, or, finally, in the case of electric steering, actuates the coder ring of a sensor device delivering a signal to the electric operating motor, combinations of these three types being possible.
In the case of purely electric steering, used increasingly commonly in handling plant such as forklift trucks, the shaft is used to connect the steering wheel to the vehicle via rolling bearings. A system for detecting the turning of the wheel, which may or may not be incorporated into the bearing, delivers a signal that represents the turning of the wheel intended for the device for guiding the roadwheels of the vehicle. Added to this is generally a system for braking the steering wheel which is intended to generate therein a resistive torque so as to enhance the accuracy with which the vehicle can be steered. A device of this type is described in document DE-A-195 10 717.
Although technically satisfactory, this device has certain disadvantages of axial bulk and of cost because of the presence of two bearings, of a braking system and of the wheel itself.
Given that the wheel no longer has any direct mechanical link with the members it is controlling, for example the roadwheels, there are two types of problem that need to be solved: on the one hand, that of limiting the number of possible revolutions performed by the wheel and, on the other hand, that of automatically returning the wheel to the neutral point when the operator stops turning the wheel.
Devices for returning to the neutral point already exist (see, in particular, documents U.S. Pat. No. 5,050,443, NO 101790), but these are designed for systems controlled by a central shaft, which is precisely what we are looking to avoid. In addition, these devices have a great many parts and are therefore expensive to manufacture.
It is an object of the present invention to overcome the abovementioned drawbacks.
An object of the present invention is to propose a simple and compact mechanism for returning to the neutral point, suited to a steering wheel that has no central shaft.
The device according to the invention is used for returning to the neutral point the rotating race of a rolling bearing provided with an inner race and with an outer race, one of the races being secured to a fixed element and the other race being secured to a rotating element. The device is of the type comprising springs intended to apply a return torque to the rotating race so as to return it to the neutral point and means for limiting, in both directions, the rotation of the rotating race. The device comprises a plate mounted so that it can rotate with respect to the fixed element and two spiral springs, a first spring being arranged on one side of the plate and fixed to the latter by its inner end, a second spring being arranged on the other side of the plate and fixed by its inner end to the fixed element, the outer end of the first spring being connected, in a first direction, to the rotation of the rotating race, and the outer end of the second spring being connected, in a second direction opposite to the first, to the rotation of the plate.
Advantageously, said device is of a diameter smaller than or equal to the size of the rolling bearing, possibly smaller than or equal to the bore of the inner race of the bearing.
Advantageously, the device comprises first means for driving the outer end of the first spring, the first drive means being secured to the rotating race, and second means for driving the outer end of the second spring, the second drive means being secured to the plate.
Advantageously, the device comprises a drive member secured to the rotating race and intended to drive the plate in a first direction of rotation by direct contact with a bearing member of said plate, the bearing member also forming a stop for stopping the rotation of the rotating race after approximately one revolution in the second direction from the neutral point.
In one embodiment of the invention, the means for driving the first spring consist of the drive member secured to the rotating race. The drive member secured to the rotating race may be a radial lug.
In another embodiment of the invention, the means of driving the first spring consist of a hole in which the outer end of the spring becomes lodged.
Advantageously, the plate comprises, on the same side as the second spring, a stop member intended to collaborate with a stop of the fixed element so as to limit to approximately one revolution the rotation of the plate when said plate is driven in the first direction of rotation and to prevent said plate from rotating from the neutral point in the second direction of rotation.
In one embodiment of the invention, the means of driving the second spring which are secured to the plate consist of the stop member situated on the plate. The stop member situated on the plate may be an axial lug.
In one embodiment of the invention, the anchoring point for the inner end of the second spring is on a fixed pin secured to the fixed member.
As a preference, the rotating of the rotating race in the first direction causes the plate to rotate and causes the second spring to become stressed by winding up without the first spring undergoing any change in stress, while rotating the rotating race in the second direction causes the first spring to become stressed by winding up without the second spring undergoing any change in stress, the plate being prevented from rotating by the stop member coming to bear against the stop of the fixed element.
In one embodiment of the invention, the second spring is arranged axially between said plate and the fixed element.
Another subject of the invention is a system involving a wheel, of the shaftless type, fixed to the rotating race of a rolling bearing equipped with a device for returning to the neutral point.
The steering wheel device with return to the neutral point is particularly axially compact by comparison with the conventional device. In addition, as the rolling bearing may have a large diameter, greater than the diameters conventionally used, while at the same time remaining smaller than the diameter of the wheel, and therefore without increasing the radial bulk, it is possible to use a high-resolution sensor, the number of pulses delivered by the encoder for a given angle of rotation being higher than for an encoder of small diameter.
The large diameter of the bearing makes it easier for a simple system that generates a braking torque to be incorporated into it, the braking force required by the generating system being inversely proportional to the diameter for a given torque.
The central zone of the wheel which is free of solid shaft offers an empty space that can be used to house auxiliary devices.
Finally, this steering wheel device can be adapted to and easily mounted at numerous possible sites on the vehicle, for example on the dashboard, via the housing that forms the support. Just a few screws are enough to secure the steering wheel via the housing.